A new version of the Claisen rearrangement is described which attaches, in high yield, an allyl group to a ring junction. A detailed study of this reaction in several polycyclic systems is proposed, the major goal of which is the determination of the factors which control its stereochemical outcome. Finally, schemes for utilizing this new reaction are proposed for the total synthesis of the potent anti-viral agent aphidicolin the plant-growth hormone gibberellic acid and the novel sesquiterpene prezizaene.